1. Field of the Invention
The present invention relates to an ink jet printer and its control method in which ejection timing of ink ejected from a nozzle disposed to an ink jet head can be adjusted within a range of one dot.
2. Description of the Related Art
In general, an ink jet printer is used as an output device of a computer, a word processor, or the like.
In a conventional ink jet printer, a carriage shaft is disposed in a direction parallel with a platen, and a reciprocatable carriage is disposed along the carriage shaft. Moreover, an ink jet recording head is mounted on the carriage to oppose to the platen in such a manner that a head nozzle of the ink jet faces a printing face of the platen.
According to the above conventional ink jet printer, a recording sheet is conveyed between the platen and the ink jet head. While the carriage having the ink jet head mounted thereon moves along the platen, the nozzle of the ink jet head is operated on the basis of a predetermined printing signal, so that the desired ink is ejected or discharged from the nozzle toward the recording sheet on the platen. Thus, a desired image is recorded or printed on the recording sheet.
In such conventional ink jet printer, when a plurality of ink jet heads are arranged at constant intervals in reciprocating direction of the ink jet heads, the mounting interval of each ink jet head needs to be constant, but there is a limitation to mounting accuracy of the ink jet head. Therefore, in some cases, the mounting interval of each ink jet head is not constant, and its mounting position is deviated. If recording is performed using such ink jet head, a recorded dot is deviated in the moving direction of the ink jet head, in accordance with the deviation of the ink jet head. As a result, the quality of the recorded image is disadvantageously deteriorated.
In this case, when the position of the ink jet head is deviated just in units of one dot, the problem can be solved in the conventional device by performing control in such a manner that the recording timing is shifted in units of dots. However, a deviation less than one dot size cannot be settled.
The present invention has been accomplished in consideration of the aforementioned circumstances, and a first object thereof is to provide an ink jet printer control method in which even when the mounting position of an ink jet head is deviated within a range of one dot, ejection timing is adjusted, so that adequate recording can be performed without any dot deviation and recorded image quality can be enhanced. A second object of the present invention is to provide an ink jet printer for direct use in implementation of the method.
The first object of the present invention is attained by the provision of a control method of an ink jet printer having a plurality of ink jet heads which are mounted on a carriage reciprocating in direction substantially orthogonal to conveying direction of a recording sheet and are deviated in the reciprocating direction of the carriage, comprising the steps of:
dividing ejection time width for recording one dot by ejecting ink from each ink jet head into plural pitches;
associating each pitch with an address of a timing data memory;
storing data indicative of ejection timing of each ink jet head in the corresponding address of said memory; and
reading the data indicative of said ejection timing from said memory in address order to independently control the ejection timing of each ink jet head.
Moreover, the first object can be attained by a control method of an ink jet printer having a plurality of ink jet heads which are mounted on a carriage reciprocating in direction substantially orthogonal to conveying direction of a recording sheet and are deviated in the reciprocating direction of the carriage, comprising the steps of:
associating the same ejection timing of each of said ink jet heads with a different bit to form one byte;
storing timing data with the number of bytes larger than the number of bytes necessary for determining ejection time of one dot into a timing data memory, an address position in said timing memory being associated with the ejection timing;
storing data indicative of the ejection timing of each ink jet head, into an address corresponding to the ejection timing of each ink jet head in the timing data memory; and
reading content of said timing data memory for one dot in address order to independently control the ejection timing of each ink jet head.
RAM (Random Access Memory) for recording the record data for one scanning operation may also be used as the timing data memory. Moreover, while the record data for one dot is read and written into a shift register, the timing data is read in the address order to obtain the ejection timing, and the amount or color of ink corresponding to the record data is controlled to be ejected at the obtained ejection timing. The record data may include information for setting different ink ejection time lengths for one dot, while the timing data may include a plurality of ejection timings different in the ejection time length.
For example, the record data may include long record data indicative of a long ejection time and short record data indicative of a short ejection time. The timing data may include long ejection start data for starting ejection early when performing the ink ejection in the long ejection time, short ejection start data for starting ejection late when performing the ink ejection in the short ejection time, and ejection end data indicating the end of the long or short ejection time. In this case, the ink ejection amount for one dot can be changed by changing the ejection time length. Especially, in case of color display with overlapped ink of a plurality of different colors for one dot, the excessive ink amount is appropriately prevented by shortening the ejection time length.
The data indicative of the ejection timing for each ink jet head is used for changing the address in the timing data memory to change the ejection timing. Therefore, when the address for storing the data indicative of the ejection timing can be changed for each ink jet head, the ejection timing of each ink jet head can independently and easily be changed, which is convenient.
According to the present invention, the second object is attained by an ink jet printer having a plurality of ink jet heads which are mounted on a carriage reciprocating in direction substantially orthogonal to conveying direction of a recording sheet and are deviated in the reciprocating direction of the carriage, comprising:
CPU for outputting record data;
a record data memory for sequentially storing a predetermined volume of record data while said ink jet heads are moving along a recording path;
a timing data memory for dividing ejection time width for recording one dot by ejecting ink from each ink jet head into a plurality of pitches, associating each pitch with an address position and for storing data indicative of ejection timing in an address corresponding to the ejection timing of each ink jet head;
a timing signal generating circuit for reading and outputting the record data for one dot corresponding to each ink jet head from said record data memory, and for reading data indicative of the ejection timing of each ink jet head from said timing data memory to output an ejection signal at a predetermined ejection timing corresponding to each ink jet head; and
a head driver for operating each ink jet head based on said record data for one dot and said ejection signal corresponding to each ink jet head to eject the ink corresponding to said record data at said predetermined ejection timing.
The record data memory and the timing data memory may be shared for use by dividing the common memory (RAM or the like) into different storage areas for use. The record data of the ink jet head for one scanning operation is stored in the memory, and the record data is rewritten every time recording of one scanning operation is finished. Additionally, once the timing data is set, the same timing data is constantly used thereafter. When a plurality of, e.g., two memories are provided, the record data can be alternately rewritten corresponding to repetition of the scanning operation. In this case, while recording is performed by the ink jet head using one of the memories, next new record data can be written into the other memory. Therefore, data processing is smoothly performed, and processing rate can be raised.
Additionally, the record data for one scanning operation herein indicates record data for one line when one head nozzle is assembled in each ink jet head. When a plurality of, e.g., four head nozzles are assembled in each ink jet head, however, four lines are simultaneously recorded. In this case, the record data indicates record data for four lines.